Using the QEI with an optical rotary encoder

leo838 — Sat, 28 Apr 2018 19:09:51 GMT

Hello all,

Has anyone had any luck using the quadrature encoder interface (QEI ) with a optical rotary encoder (similar to the Grayhill 62P series) ?

I've been trying without much luck, it seems its designed for motor control but I'm hoping to get it working with the above encoder.

Thanks,

Leo

Re: Using the QEI with an optical rotary encoder

leo838 — Mon, 30 Apr 2018 09:01:27 GMT

Actually I got it working with a straightforward implementation below:

/*
===============================================================================
Name        : LPC1769Template.c
Author      : OH
Version     :
Copyright   : $(copyright)
Description : Implementation of an optical decoder on using the QEI on a LPC1769
===============================================================================
*/

#ifdef __USE_CMSIS
#include "LPC17xx.h"
#endif

#include <cr_section_macros.h>

// TODO: insert other include files here
#define RESET_VALUE 0x7FFFFFFF

volatile int new_pos = 0;   // Use to increment/ decrement position on interrupt
volatile int old_pos = 0;

void qei_setup(void){
   // setup for Grayhill series 62P optical encoder

   LPC_SC->PCONP    |= 1<<18;         // Power up QEI
   LPC_SC->PCLKSEL1 |= 3;             // Select clock for QEI = cclk/8
   LPC_PINCON->PINSEL3 |= (1<<8);     // configure as MCI0-QEA - P1.20 -> Pad 7 on LPCXpresso 1769
   LPC_PINCON->PINSEL3 |= (1<<14);    // configure as MCI1-QEB - P1.23 -> Pad 6 on LPCXpresso 1769
   //LPC_PINCON->PINSEL3 |= (1<<16);    // configure as MCI2-INDX - P1.24

   LPC_QEI->QEICONF |= (1<<2);        // Set quadrature mode - 4x mode
   LPC_QEI->QEIMAXPOS = RESET_VALUE; // Maximum pulse count limit after which counter resets
   LPC_QEI->FILTER     = 0;          // Number of clk delays to delay before accepting input

   //Enable interrupts on postions
   //LPC_QEI-> QEIIES |= (1 << 6) | (1 << 7) | (1 << 8); // Enable interrupts on position captures

   //NVIC_EnableIRQ(QEI_IRQn);   // Enable interrupt

}

void led_setup(void){
   LPC_GPIO0->FIODIR |= (1 << 22); //Configure P0.22 as output, position 0, Red
   LPC_GPIO3->FIODIR |= (1 << 26); //Configure P3.26 as output, position 1, Blue
   LPC_GPIO3->FIODIR |= (1 << 25); //Configure P3.25 as output, position 2, Green
}

void QEI_IRQHander(){
   // Not used!!
   if ((LPC_QEI-> QEIINTSTAT >> 6) & 1){
       // Position 0
       new_pos = 0;
       LPC_QEI-> QEICLR |= (1<<6);
   }
   else if ((LPC_QEI-> QEIINTSTAT >> 7) & 1){
       // Position 1
       new_pos = 1;
       LPC_QEI-> QEICLR |= (1<<7);
   }
   else if ((LPC_QEI-> QEIINTSTAT >> 8) & 1){
       // Position 2
       new_pos = 2;
       LPC_QEI-> QEICLR |= (1<<8);
   }else {
       LPC_QEI-> QEICLR |= (1<<3) | (1 <<5);   // TODO: Clear dir & clock pulse
   }
}

int main(void) {

   qei_setup();
   led_setup();
   old_pos = LPC_QEI->QEIPOS;

    while(1) {

       new_pos = (LPC_QEI->QEIPOS - old_pos);

       if (new_pos > 0){
           // clockwise rotation?
           //LPC_GPIO0->FIOPIN = (1 << 22); // On
           LPC_GPIO3->FIOCLR = (1 << 25); // Off
           LPC_GPIO3->FIOPIN = (1 << 26); // Blue On

           old_pos = LPC_QEI->QEIPOS;
       }
       else if (new_pos < 0){
           //LPC_GPIO0->FIOCLR = (1 << 22);
           LPC_GPIO3->FIOPIN = (1 << 25); // Green On
           LPC_GPIO3->FIOCLR = (1 << 26); // blue off
           old_pos = LPC_QEI->QEIPOS;
       }
       else{
           //LPC_GPIO0->FIOCLR = (1 << 22);
           //LPC_GPIO3->FIOCLR = (1 << 25);
           //LPC_GPIO3->FIOCLR = (1 << 26);
       }

    }
    return 0 ;
}

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Using the QEI with an optical rotary encoder

Re: Using the QEI with an optical rotary encoder